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A289991 Number of unlabeled connected simple graphs with n nodes of degree 4 or less and with at least a cyclic structure and a node of degree one. 2

%I #28 Mar 20 2020 23:33:18

%S 0,0,0,1,7,35,181,1027,6551,47356,383353,3439508,33796286,360254030,

%T 4132780425,50700507116,661702767423,9148018231984,133481943863634,

%U 2049205561735698,33008193951255524,556509843849858317,9799223447550907197,179855583136712491494

%N Number of unlabeled connected simple graphs with n nodes of degree 4 or less and with at least a cyclic structure and a node of degree one.

%C Number of alkyl-n-cycloalkanes with n carbon atoms (the pure n-cycloalkanes aren't counted here).

%C Stereoisomerism is not taken into account. Some of the drawn structures may or may not exist due to their strained geometries.

%F a(n) = A289159(n) - A289990(n).

%F a(n) = A121941(n) - A006820(n) - A289989(n). - _Andrew Howroyd_, Mar 20 2020

%e a(5) = 7 because there are 7 structures with 5 carbons following the rule above: 1,1-dimethylcyclopropane, 1,2-dimethylcyclopropane, ethylcyclopropane, methylcyclobutane, 1-methylbicyclobutane, 2-methylbicyclobutane, methyltetrahedrane.

%Y Cf. A006820, A121941, A289159, A289989, A289990.

%K nonn

%O 1,5

%A _Natan Arie Consigli_, Aug 03 2017

%E a(0) removed and a(15)-a(24) from _Andrew Howroyd_, Mar 20 2020

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Last modified March 28 15:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)